In the foundry industry, one of the processes used for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry mix which is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.
One of the processes used in sand casting for making molds and cores is the no-bake process. In this process, a foundry aggregate, binder, and liquid curing catalyst are mixed and compacted to produce a cured mold and/or core. In the no-bake process, it is important to formulate a foundry mix which will provide sufficient worktime to allow shaping. Worktime is the time between when mixing begins and when the mixture can no longer be effectively shaped to fill a mold or core.
A binder commonly used in the no-bake fabrication process is a polyurethane binder derived from curing a polyurethane-forming binder composition with a liquid tertiary amine catalyst. The polyurethane-forming binder composition usually consists of a phenolic resin component, a polyisocyanate component, and a catalyst component. Such polyurethane-forming binder compositions, used in the no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 1370.degree. C. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 815.degree. C.
Binders are needed which result in higher productivity in core and mold making and metal casting. To accomplish this, the cores and mold produced with the binder must have high tensile strengths when demolded to allow faster demolding and fewer broken molds. Good resistance to humidity also is important because this minimizes breaking under hot and/or humid conditions. These properties must be obtained without shortening the worktime and striptime of the cores and molds. Without adequate worktime and striptime, the operator making the cores and molds cannot be effective.